Shanling UA5 - Portable USB DAC/AMP 4.4mm Balanced Hybrid Battery Power | eBay
USB-C Audio Interface w/USBAdt | Saramonic
Amazon.com: ILIWIWY Hi-Fi Headphone Amplifier Buit-in Power Bank Portable 3.5mm Stereo Audio Out Powered by Lithium Battery Headset Support GAIN/BASS for Android phone/iPhone/iPad/MP3/MP4/Laptops and PCs, etc. : Electronics
iFi Audio xDSD Portable USB DAC and headphone amplifier with Bluetooth® at Crutchfield